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GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
GEOG 100--Weathering and Mass Wasting (F'13)
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GEOG 100--Weathering and Mass Wasting (F'13)

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Transcript

  • 1. Weathering and Mass Wasting Chapter 10
  • 2. External vs. Internal Processes (the dynamic equilibrium model) (the dynamic equilibrium model) 2
  • 3. Dynamic Equilibrium • Equilibrium stability (fluctuating around some average) [Geomorphic threshold is reached] • Destabilizing event • Adjustment • New condition of equilibrium stability 3
  • 4. The Grand Canyon 4
  • 5. Denudation—Large-scale removal of material that lowers the overall profile of the topography 5
  • 6. Denudation Processes • Weathering—The combined action of all atmospheric and biologic processes that cause rock to disintegrate physically and decompose chemically because of exposure near Earth’s surface (from bedrock to regolith) • Mass wasting—spontaneous downslope movement of soil and eroded rock fragments under the influence of gravity, but without the action of moving air, water or ice • Erosion—extensive removal of rock material, generally transported long distances 6
  • 7. Weathering of Bedrock ► Wherever bedrock is exposed to the natural elements, it weathers ► Any crack, joint, or cavity in the rock will allow weathering agents to penetrate and break it apart 7
  • 8. Jointing in Bryce Canyon, UT
  • 9. As rocks weather, surface area increases, offering more surfaces to be weathered…
  • 10. …producing this result.
  • 11. Mechanical Weathering • Physical disintegration of rock as a result of natural phenomena, without a change in its chemical composition – Pounding, pushing, cracking, breaking, wedging apart 13
  • 12. Mechanical Weathering Processes • • • • • Frost wedging Salt wedging Unloading/pressure-release jointing Thermal expansion and contraction Biologic weathering
  • 13. Frost Wedging • Repeated growth and melting of ice crystals in pore spaces of rock fractures or joints • Expanding ice exerts pressure, breaking rocks apart • Most effective where there is repeated freeze and thaw (as in arctic or tundra environments)
  • 14. Frost Wedging
  • 15. Salt Wedging • Similar to frost wedging • Growth of salt crystals breaks rocks apart • Most effective in coastal environments and semi-arid environments Honeycomb (tafoni), Salt Point, Sonoma Coast
  • 16. Unloading or Pressure-release jointing • Rock brought near the surface as the rocks above (or even glaciers) erode away relieves confining pressure and allows the rock to expand slightly, forming cracks – Sheeting—The breaking away of layers of rock in sheets, caused by expansion, usually from unloading processes • Exfoliation dome—Sheeting on a massive scale, over the face of a large segment of rock (Half Dome in Yosemite, Sierra Nevada Mtns.) 18
  • 17. Thermal Expansion and Contraction • When rock is heated, it expands slightly, and when cooled, it contracts • Rapid expansion and contraction of the surface of the rock causes cracks to form and propagate • Most effective in regions with large differences in temperature between daily highs and nightly lows
  • 18. Thermal Expansion and Contraction
  • 19. Biologic Weathering • Growth of plant roots, burrowing animals • Pressure is exerted by the growth of tiny rootlets in joint fractures, which causes the loosening of small rock particles and mineral grains • Burrowing animals such as squirrels and oysters may also erode rocks
  • 20. Chemical Weathering • Decomposition of rock through chemical alteration of its minerals • Exposed to water or other solutions, minerals in rocks undergo a chemical change, weakening internal structures – Air, soil water solutions, and groundwater solutions contain dissolved oxygen, carbon dioxide, or other reactive elements – Water is the greatest agent of chemical weathering
  • 21. Chemical Weathering: The Influence of Temperature and Precipitation Chemical weathering is most effective in warm, moist climates
  • 22. Oxidation • Oxygen dissolved in soil water or ground water can bond with the chemical elements of the minerals to form new minerals • Causes expansion and exerts pressure that breaks the rocks apart • Example: iron (Fe) turning to rust (Fe2O3) in the presence of oxygen and water
  • 23. Hydrolysis and Hydration • Hydrolysis--minerals reacting with water split into other compounds (may also split the water molecules) – granite: feldspar turns to clays + quartz sand – contributes to spheroidal weathering
  • 24. Hydrolysis and Hydration • Hydration--The whole water molecule forms chemical bonds to become part of the chemical composition of the rock, causing expansion and grain-by-grain destruction of rocks Formation of gypsum from anhydrous calcium sulfate (the mineral anhydrite) which has absorbed water into its chemical structure
  • 25. Carbonic Acid Carbon dioxide dissolved in water creates a weak acid called carbonic acid which can dissolve some minerals, especially calcium carbonate Limestone and marble are most susceptible to this type of weathering
  • 26. Acid Precipitation • Urban pollution from sulfur and nitrogen oxide gases mixes with atmospheric water, forming acid precipitation • Dissolves limestone and marble (often used for public statues and tombstones) and other types of building stones; destroys vegetation, affects human health
  • 27. Organic Acids • Decaying vegetation mixes w/ water to form soil water w/ complex organic acids that can react to dissolve or chemically alter minerals
  • 28. Mass Wasting • Material is moved a short distance down a slope under the influence of gravity • Angle of repose—the steepest angle that loose fragments can lie without movement if undisturbed
  • 29. 31
  • 30. Mass Wasting • The type of mass wasting event that occurs will depend upon speed and the degree of saturation
  • 31. Mass Wasting (another view)
  • 32. Types of Mass Wasting • Rock fall • Rock slide and Topple • Slump • Solifluction • Creep • Debris flow • Earth flow • Mudflow • Induced mass wasting
  • 33. Rock Fall Talus slopes—Regolith which has fallen down steep slopes, funneled into “blankets” of rock called talus cones Fresh slopes are very unstable
  • 34. Rock Fall
  • 35. Rock Slide
  • 36. Mudflow and Debris Flow • Mudflow—Rainwater mixed with soil flowing very quickly downslope as a river of mud – Usually in canyons of mountainous regions – Can carry large objects, destroying property and taking lives – Flows until mud thickens, slows, and eventually stops • Debris flow—More rock fragment than mudflow, but similar in other characteristics
  • 37. Earthflow • Water-saturated soil or rock material • Moves a limited distance down slope as one large mass • Generally slower in motion (over the course of hours) • Common form of earth movement causing road closures and property destruction during heavy rains
  • 38. Near La Conchita Slide, along Hwy. 101 in Ventura County Hwy. 101 in Ventura County
  • 39. La Conchita Slide (Earthflow) Hwy. 101, Ventura County
  • 40. La Conchita Slide (Earthflow) Hwy. 101, Ventura County
  • 41. Slump—Slow, concave sliding
  • 42. Slump
  • 43. Slump
  • 44. Solifluction • Continuous freeze and thaw cycles slowly move weathered particles downslope • Over time, the entire slope moves downhill
  • 45. Solifluction
  • 46. Solifluction
  • 47. Soil Creep
  • 48. Induced Mass Wasting Mass wasting caused by human activity • Moving weathered rock material downslope during construction on steep hillsides – Carried away as debris flows or mudflows during heavy rains • Removal of material supporting the base of a slope • The wetting of weathered rock material and soil from pipe breakage, lawn watering, etc. causing slippage • Debris removal by heavy rains after fire may also remove stabilizing vegetation
  • 49. Induced Mass Wasting: Construction of the Panama Canal

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